Ferrous Fumarate Dosing for Iron Deficiency Anemia
For treating iron deficiency anemia in adults, start with one 210 mg ferrous fumarate tablet (69 mg elemental iron) once daily, or alternatively one 322 mg tablet (106 mg elemental iron) once daily. 1
Standard Dosing Regimen
Initial treatment should be 50-100 mg elemental iron once daily, which translates to one 210 mg ferrous fumarate tablet (69 mg elemental iron) or one 322 mg tablet (106 mg elemental iron) taken once daily 1, 2
Take on an empty stomach (fasting state) for optimal absorption 2
Once daily dosing achieves similar hemoglobin response as multiple daily doses but with significantly better tolerability 2
If Side Effects Occur
Switch to alternate-day dosing (100-200 mg elemental iron every other day) if gastrointestinal side effects develop 1, 2
Alternate-day administration significantly increases fractional iron absorption compared to daily dosing and reduces GI adverse events (relative risk 0.56) 1, 2
Do not switch between different ferrous salts (sulfate, fumarate, gluconate) for intolerance—this is not evidence-based; instead use alternate-day dosing, ferric maltol, or parenteral iron 2
Monitoring and Duration
Check hemoglobin at 2 weeks: Failure to achieve at least 10 g/L rise strongly predicts subsequent treatment failure (sensitivity 90.1%, specificity 79.3%) 1, 2
Formal response assessment at 4 weeks: No hemoglobin response after 4 weeks indicates need for parenteral iron 1, 2
Continue treatment for 3 months after hemoglobin normalizes to adequately replenish iron stores 1, 2
Monitor blood counts every 4 weeks until hemoglobin normalizes 2
Special Populations
Women of Reproductive Age (Menstruating)
- Require higher doses: 50-100 mg elemental iron daily, which equals two 210 mg ferrous fumarate tablets daily 1
Pregnancy and Lactation
- Increased requirements necessitate additional supplementation beyond standard doses 1
Post-Bariatric Surgery
- Oral iron absorption is significantly impaired; consider intravenous iron as first-line rather than oral formulations 1
Absorption Enhancement
Taking with citrus fruits/drinks or 250-500 mg vitamin C may enhance absorption, though clinical effectiveness evidence is limited 1, 2
Separate iron and calcium supplements by 1-2 hours to avoid absorption interference 1
When to Use Intravenous Iron Instead
Switch to parenteral iron when: 1, 2
- No hemoglobin response after 4 weeks of adequate oral therapy
- Oral iron is not tolerated despite alternate-day dosing
- Impaired absorption (celiac disease, inflammatory bowel disease, post-bariatric surgery)
- Active inflammatory bowel disease
- Ongoing blood loss exceeding oral iron absorption capacity
- Severe symptomatic anemia requiring rapid correction
Common Pitfalls to Avoid
Never prescribe divided daily doses (e.g., three times daily)—this reduces absorption due to hepcidin elevation and increases side effects 2
Do not stop treatment when hemoglobin normalizes—continue for 3 months to replenish iron stores 1, 2
Do not use modified-release preparations—they are less suitable for prescribing 1
Cost Considerations
Ferrous fumarate is cost-effective at approximately £1.00-£1.40 per 28 days for standard preparations, compared to £47.60 for ferric maltol 1